This class can be use to manipulate hierarchic trees of records stored in a MySQL database using Joe Celko visitation model.

It can perform the following tasks in a very effecient way mostly using one SELECT query statement:

- Find out leaf nodes in the current tree (nodes have no children)
- Find out nodes of a sub-tree for given node
- Find out the context path of given node
- Find out the level or depth of a given node
- Find out how many descendants a given node has